1. Field of the Invention
The field of the present invention is parking meters and more particularly to the use of electronically operated parking meters coupled with a sensor for positively sensing unobtrusively the presence or absence of a vehicle in a specified parking space controlled by the sensor and electronically operated parking meter. In the present invention an induction coil mounted below the surface of the parking area is used to provide positive signals to the electronically operated parking meter and a cpu upon both the entrance of a vehicle into the parking space and the movement of the vehicle from the parking space.
Moreover, the detecting system is battery operated and the battery life is extended by duty cycle operation of the detector system, whereby only a small portion of a detecting cycle is actually employed for detecting the status of the parking space.
2. Related Art
Parking meters have traditionally been used to raise revenue. Such devices have included a timer and a winding mechanism requiring coins. More recently, electronic meters have been developed which include an electronic timer with an LCD time indicator.
With the advent of the electronic meter, attempts have been made to make the meter interactive with vehicle traffic in the associated parking space. One way to obtain information about vehicle traffic at parking spaces is to couple the parking meter to a vehicle sensor. The vehicle sensor can detect when a vehicle enters a parking space as well as when the vehicle leaves. One such system uses an infra-red light beam to detect vehicle presence at a parking space.
Individual parking meter systems have each utilized different vehicle sensors, such as an infra-red light beam, ultrasonic systems and inductance type sensors to detect the presence or absence of a vehicle in an associated parking space.
One problem with light beam detection is that the beam does not distinguish between a vehicle and any other solid object. Thus, the system could be disabled by simply covering the window from which the light beam is emitted with a piece of tape or cardboard. In addition, false activity could occur with the opening of a door or other movement in front of the meter sensor. Even temperature or humidity changes could cause problems. Consequently, interest remains in developing an electronically controlled parking meter system that overcomes the aforementioned problems and is capable of accurately detecting vehicle traffic at a parking space.
There are a number of known parking meter vehicle detector systems, namely:
(1) U.S. Pat. No. 3,873,964; Vehicle Detection; Potter
The loop oscillator of the vehicle detector system continually oscillates at the resonant frequency during normal operation of the system and digital circuitry in the system measures the frequency of the loop oscillator by a cycle-counting technique. An automatic timing circuit generates a reference frame time for the frequency counting measurement. The reference frame time is a function of the desired operational sensitivity of the system and of the resonant frequency of the loop and lead-in loop oscillator frequency-determining circuit. A vehicle is detected whenever an increase of loop oscillator frequency counts occurs from one reference frame time to the next, and when that increase exceeds a predetermined threshold.
(2) U.S. Pat. No. 3,875,555; Vehicle Detection System; Potter; Indicator Controls, Corp.
The magnetic inductance vehicle detection system includes an embedded wire loop to sense the presence of a vehicle in a roadway. A first oscillator connected to the loop changes frequency as the loop inductance changes due to the presence of a vehicle. A second oscillator with a frequency independent of the loop inductance is used as a reference. Logic circuitry emits a signal whenever the oscillator loop frequency exceeds a predetermined frequency beyond a predetermined frequency differential.
(3) U.S. Pat. No. Re29511; Parking Meter; Rubenstein
The parking meter electrically indicates “remaining time” and electrically operates only in the presence of a vehicle and when there is “paid-for” time on the meter. Unused time by one departing motorist is cancelled.
(4) U.S. Pat. No. 3,943,339; Inductive Loop Dectector System; Koerner et al.; Canoga Controls Corporation
An oscillator circuit is operatively connected to each one of multiple inductance loops each located in a given space in a roadway and the loop frequency is monitored by a counter measuring the time duration or period of loop oscillator cycles. The monitored oscillator cycle is then compared with a reference duration to determine whether the loop oscillator frequency has increased or decreased.
(5) U.S. Pat. No. 3,989,932; Iductive Loop Vehicle Detector; Koerner; Canoga Controls Corporation
Oscillator circuitry is connected to an inductance loop for detecting the presence of vehicles and the loop frequency is monitored by a loop counter for counting the loop oscillator cycles. A duration counter measures the time duration of a fixed number of loop oscillator cycles and the count is compared with an adaptable reference duration to determine an increase or decrease in the loop inductance, thereby determining the presence or absence of a vehicle in the inductance loop.
(6) U.S. Pat. No. 4,358,749; Object Detection; Clark; Redland Automation Limited
An inductive sensing loop is connected with an oscillator provided with a voltage controlled capacitor in a phase locked loop providing a reference frequency (VCO). The voltage of the capacitor varies in the presence of a vehicle and this varying voltage is applied to an auxiliary VCO whose frequency is accordingly varied and analyzed for detection purposes. A microcomputer includes a clock source that is a reference frequency source.
(7) U.S. Pat. No. 4,472,706; Vehicle Presence Loop Detector; Hodge et al.; Not Assigned
A tuned circuit having a magnetic field-producing induction loop produces changing signals in the presence of a vehicle. A first signal amplifier amplifies the signal from the loop and a second amplifier responds to the positive or negative polarity input from the first amplifier to provide an output in response to a rapidly changing input which activates a logic gate for sensing the polarity of the second amplifier output and producing a gated output signal indicative of the presence or absence of a vehicle within the loop.
(8) U.S. Pat. No. 4,491,841; Self-Adjusting Inductive Object-Presence Detector; Clark; Sarasota Automation Limited
An oscillator includes an inductive sensing loop and a first counter samples the oscillator frequency or period and the resulting count is applied as a preset reference to a second counter which is counted down in one sample period while a new count is counted by the first counter. The residue in the second counter at the end of a sample period is indicative of the presence or absence of a vehicle. Provision is made for detection of the departure of a vehicle by use of additional counters.
(9) U.S. Pat. No. 4,680,717; Microprocessor Controlled Loop Detector System; Martin; Indicator Controls Corporation
A microprocessor-controlled loop detection system is connected to a number of inductive loops which are individually located to detect the presence of motor vehicles above the loops to control motor vehicles at a traffic intersection. A common oscillator is connected to each loop on a time shared basis and the microprocessor counts the number of cycles of the oscillator output signal to determine the oscillator frequency.
(10) U.S. Pat. No. 5,153,525; Vehicle Detector with Series Resonant Oscillator Drive; Hoeckman et al.
The series resonant oscillator circuit drives an inductive load including an inductive sensor and a detection system using the series resonant oscillator circuit and inductive sensor. An inductive load is connected in the series path with a capacitative impedance. An oscillator signal provides power to the series path and is controlled as a function of current sensed in the series path. The frequency of the oscillator signal changes as a function of changes in the inductance of the inductive sensor.
(11) U.S. Pat. No. 5,570,771; Electronic Parking Meter and System; Jacobs
The parking meter system uses a low-current drain electronic parking meter and a mobile transceiver. A sonar transducer detects the presence of a vehicle in an adjacent parking space and an infra red transceiver communicates with the mobile transceiver. A microprocessor responds to electrical signals from the various detectors to provide data displayable on a display and transmittable by the IR transceiver to the mobile transceiver. The meter is entirely battery operated and can operate for an extended period of time, for example, six months to one year, without battery replacement.
(12) U.S. Pat. No. 5,903,520; Electronic Module for Conventional Parking Meter; Dee et al.
The electronic module comprises a shell attachable to a conventional parking meter and a meter condition sensor for detecting, from a distant point, time and violative conditions of the parking meter with the indicator in an indicating mode, and an ultrasonic vehicle sensor affixed to the shell for detecting a parked vehicle. The electronic module further includes electronic circuitry with a power source for operating the module; means for receiving a first signal from the meter condition sensor and a second signal from the vehicle sensor; means for processing the first and second signals and means for transmitting a coded message to a remote receiver.
(13) U.S. Pat. No. 5,936,551; Vehicle Detector with Improved Reference Tracking; Allen & Potter
A vehicle detector having improved reference tracking routines in both the NO CALL and CALL directions and wherein CALL direction tracking includes rate sensitive tracking wherein the reference is only changed in response to small fluctuations in loop frequency due to drift, and one or more fixed decrementing tracking intervals during which the reference is decremented at a fixed rate for a maximum predetermined period of time. CALL direction tracking also included infinite tracking during which the reference is decremented to an end value representative of loop inductance prior to the end value representative of loop inductance prior to the generation of a CALL signal. No CALL tracking enables reference updating only after the loop frequency has stabilized for a minimum period of time, a minimum number of loop frequency samples or both.